ETBC: COLLABORATIVE RESEARCH: MASS-DEPENDENT AND INDEPENDENT MERCURY ISOTOPE FRACTIONATION DURING MICROBIAL METHYLATION AND REDOX TRANSFORMATIONS OF MERCURY IN NATURAL WATERS

ETBC：合作研究：天然水中汞的微生物甲基化和氧化还原转化过程中质量依赖和独立的汞同位素分馏

• 批准号: 0952108
• 负责人: Joel Blum
• 金额: $ 26.24万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952108&HistoricalAwards=false
• 关键词: ETBC; COLLABORATIVE; RESEARCH; MASS; DEPENDENT

Intellectual merit: The proposed research is based on recent achievements by the PIs and others, and seeks to expand the PIs? on-going studies of isotopic fractionation during microbial and abiotic Hg transformations. During the last five years the PIs have shown that: (i) Mass dependent isotopic fractionation (MDF) occurred during the microbial reduction of ionic mercury (Hg[II]) by several bacterial strains that possess the enzyme mercuric reductase and MDF also occurred during microbial methylmercury (MeHg) degradation; (ii) Photoreduction of Hg(II) and photodegradation of MeHg caused MDF as well as mass independent fractionation (MIF) of up to 2?. Varying amounts of MIF (denoted as Ä199Hg and Ä201Hg) recorded in freshwater and marine fish tissue suggested different extents of photo degradation of MeHg prior to its incorporation into the aquatic food web. These results along with large variations in natural samples documented by the Blum lab and others, strongly suggest that the isotopic composition of Hg has the potential for distinguishing between different sources of Hg(0) emissions and pathways of Hg(II) reduction and MeHg degradation.To date, the PIs? studies have focused on Hg redox transformations and MeHg degradation. Yet, the bioaccumulation of MeHg in aquatic food webs has a profound effect on human and ecosystem health and the examination of whether or not isotope fractionation occurs during methylation of Hg is, therefore, a high priority. If significant fractionation occurs during formation of MeHg and is modulated by different environmental conditions and by the nature of the methylating processes, tools for distinguishing sources and pathways of MeHg in the environment may become available and enhance the management of Hg contaminated ecosystems. The first objective of the proposed study is the examination of isotopic fractionation during Hg methylation by sulfate and iron reducing bacteria to test the hypothesis that microbial Hg methylation results in significant MDF, but not in MIF. The second objective is the investigation ofhow environmental variables, which define freshwater and marine environments, impact MIF and MDF during Hg redox transformations to test the hypothesis that photochemical reduction, oxidation and demethylation will imprint diagnostic MDF and MIF signatures on reaction substrates and products. Finally, Hg isotopic fractionation during transformation pathways mediated by an important component of aquatic ecosystems, phototrophic planktonic organisms, has not been examined to date. The third objective addresses this lack of knowledge by testing the hypothesis that intracellular Hg(II) reduction and MeHg degradation in phytoplankton incubated in the light will result in MDF and possibly MIF. Broader Impact: The proposed research activity will continue to lay the groundwork for a new approach or the identification of sources, sinks, and pathways of Hg transformations in impacted ecosystems. This approach has the potential to significantly enhance understanding of Hg biogeochemistry on temporal and spatial scales ranging from molecular mechanisms, to ecosystems, to global cycles, and to the geological record. As ecosystem Hg contamination remains a major public health concern, this project will support implementation of sound environmental practices to reduce Hg contamination and exposure. The proposed research will train a postdoctoral fellow in the application of stable isotope-based approaches in geobiology and ecosystem processes. In addition, undergraduate and graduate students will be integrated into the project, exposing them to cutting edge concepts and technologies, which are at the interface between biology, geology and ecosystem sciences. It is at this interface that importantparadigm-shifting, research advances are being made. Undergraduate students will assist with the analytical geochemistry as part of senior thesis research projects and PhD dissertation projects. Results will be published and disseminated broadly.

智力优点：拟议的研究基于PI和其他人的最新成就，并试图扩大PI？在微生物和非生物HG转化过程中的同位素分馏的持续研究。在过去的五年中，PIS表明：（i）在微生物汞（Hg [ii]）的微生物还原过程中，几种细菌菌株在微生物减少过程中发生了质量依赖的同位素分馏（MDF），这些细菌菌株还具有降低酶的汞液化和MDF，也发生在微生物甲基汞（MEHG）期间。 （ii）Hg（II）的光电量和MEHG的光降解导致MDF以及质量独立分馏（MIF）的最高2？。在淡水和海洋鱼类组织中记录的不同数量的MIF（表示为ä199hg和ä201Hg）表明，在其工业食品网络之前，MEHG的照片降解不同。这些结果以及Blum Lab和其他人所记录的天然样品的巨大变化，强烈表明HG的同位素组成有可能区分Hg（0）Hg（II）还原和MEHG降低途径的不同来源。研究的重点是HG氧化还原转化和MEHG降解。但是，水生食物网中MEHG的生物积累对人类和生态系统的健康具有深远的影响，并且检查同位素分馏在HG甲基化期间是否发生同位素分馏，因此很高的优先级。如果在MEHG的形成过程中发生明显的分馏，并且由不同的环境条件和甲基化过程的性质进行调节，则可能可以使用以区分MEHG的来源和途径的工具，并可以增强HG污染生态系统的管理。拟议的研究的第一个目标是检查在Hg甲基化期间通过硫酸盐和铁还原细菌在HG甲基化过程中的检查，以检验以下假设：微生物HG甲基化会导致MDF显着，但在MIF中却没有。第二个目标是研究在HG氧化还原转化期间定义淡水和海洋环境的环境变量如何影响MIF和MDF，以检验以下假设：光化学还原，氧化和脱甲基化将使诊断MDF和MIF标记对反应底物和产物的诊断MDF和MIF签名。最后，迄今为止尚未检查由水生生态系统（光养浮游生物生物）介导的转化途径中的HG同位素分级。第三个目标通过检验以下假设，即在光中孵育的浮游植物中的细胞内Hg（II）减少和MEHG降解将导致MDF和可能的MIF。更广泛的影响：拟议的研究活动将继续为新方法或识别受影响生态系统中HG转化的来源，水槽和途径的识别奠定基础。这种方法有可能在临时和空间尺度上显着增强对汞生物地球化学的理解，从分子机制，生态系统到全球周期以及地质记录。由于生态系统HG污染仍然是一个主要的公共卫生问题，因此该项目将支持实施合理的环境实践，以减少HG污染和暴露。拟议的研究将培训一名博士后研究员，以在地球生物学和生态系统过程中采用稳定的基于同位素的方法。此外，本科生和研究生将被整合到项目中，将它们暴露于最前沿的概念和技术，这些概念和技术处于生物学，地质和生态系统科学之间的界面。正是在这个界面上，重要的范式转移，正在进行研究进展。作为高级论文研究项目和博士学位论文项目的一部分，本科生将协助分析地球化学。结果将被广泛发布和传播。